Inbreeding

How close together can I inbreed mice before genetics become a problem? Would males to granddaughters fathered by another male be far enough apart? I know I will have to get new males at some point, I just didn't know how far I could go with switching my breeding males back and forth. I have some girls that are serious baby makers, and I want to try to keep that going.

I have a colony of 10.60

To give you an idea I have just brought in some new blood after not doing so for 7 years and my colony is strong and without any issue (I did it because I want to breed some hairless so I bought a pair of those), of course if you have issues bringing new blood and culling animals with issue is a must, just be careful and make sure that you quarantine any new stocks.

Sometime bring in new blood can cause a lot more issues than selective and line breeding.

I had that thought, too, that bringing in new would cause more issues. I have 2 males and 3 sets of 4 females. With finally really having things going well, I was trying to plan things out a bit so that I didn't breed too close together and cause problems.

Line/inbreeding is not a problem in itself. As long as your mice do not carry the same genetic issues there will be no problem. Inbreeding will quickly help you determine if your colony has any genetic predisposition to health problems. For example, you have a doe who carries a gene for tumors and an unrelated male who doesn't. You breed them together, none of the babies have tumors, but some carry the gene for it. You could go a few more generations without having tumors pop up, and then all of a sudden you do, and a good portion of your colony carry it so you could be dealing with this issue for quite a while before you are able to cull it all out. Now lets say you had bred the doe to a brother who also carried the gene for tumors, you would have known probably in the first litter that they had that issue.

If a colony is still breeding well after 10 generations of brother x sister matings, it is likely to continue indefinitely.